An auditory ossicle prosthesis of this kind is, for example, known from German Utility Model DE 296 09 687 U1, from WO 02/069850 A1 or from U.S. Pat. No. 6,554,861 B2.
The role of the middle ear in humans, with its auditory ossicles, is to take up the sound waves impacting the tympanic membrane via the external acoustic meatus and transmit them to the fluid-filled inner ear. The three auditory ossicles are the hammer (malleus), which is attached to the tympanic membrane, the stirrup (stapes), which is connected via its footplate (basis stapedis) to the inner ear, and the anvil (incus), which is situated between the hammer and the stirrup and is connected to these in an articulated manner. In otosclerosis, a disease of the human petrous bone (the bone in which the whole ear sits), inflammatory-like processes affecting the bone may lead to a fixing of the normally loosely oscillating stirrup. As a result of this, the sound signal is not transmitted, or is transmitted only incompletely, to the inner ear via the ossicular chain, and this leads to impaired hearing.
Auditory ossicle prostheses are used to transmit sound from the tympanic membrane to the inner ear when the ossicles of the human middle ear are entirely or partially absent or damaged. The auditory ossicle prosthesis has two ends, and, depending on the individual circumstances of the patient, one end of the auditory ossicle prosthesis is fixed, for example, to the process of the anvil or to the manubrium of the hammer, and the other end is, for example, secured to the stirrup or plunged directly into the inner ear. With the known auditory ossicle prostheses, the sound conduction between the tympanic membrane and the inner ear is often made possible only to a limited extent, since these prostheses are able only to an extremely limited extent to replace the natural anatomical features of the ossicular chain.
An important problem when fitting an auditory ossicle prosthesis lies in the connection of the prosthesis to a member of the ossicular chain, since this connection should of course on the one hand be secure and permanent, but on the other hand should also be reasonably easy for the operator to establish. U.S. Pat. No. 3,711,869 A and U.S. Pat. No. 5,370,689 A, for example, have disclosed auditory ossicle prostheses that are secured on the process of the anvil by means of a slotted eyelet. However, special tools are needed to widen the eyelet and to make it easier to push the prosthesis onto the process of the anvil, and also to fix the prosthesis by pressing the slotted eyelet together, which proves quite awkward in practice.
An auditory ossicle prosthesis known from the above-mentioned German Utility Model DE 296 09 687 U1 of the Applicant is distinguished by being relatively easily to implant, by simply clipping it onto the long process of the anvil. It holds in place solely by the clamping action of the clip. No further securing means or special fixing methods are needed.
However, in the course of implantation, tilting of the prosthesis could occur, which would make the operation more difficult for the surgeon. To overcome this problem, in a “successor model” of this prosthesis, which is described in DE 202 12 771 U1, the clamp is lengthened with at least one of its legs protruding past the opening outward in the form of an arc, with which the prosthesis can be suspended, before being slipped on, from the long process of the anvil of the human middle ear, thus affording the surgeon the possibility of changing the surgical instruments and, for example, using a small hook to slip the prosthesis onto the long process of the anvil. In addition, this measure also allows the spring characteristic of the structure to be made considerable “softer”. This results in considerably improved handling of the auditory ossicle prosthesis, because greater differences in the individual shape and size of the point of attachment on the auditory ossicle of the respective patient can also be easily compensated for, without having to keep different prostheses ready.
The known auditory ossicle prostheses according to the aforementioned WO 02/069850 A1 or U.S. Pat. No. 6,554,861 B2, which are made from a shape-memory metal, can also be fixed relatively easily at a desired site of an auditory ossicle with the aid of the first securing element likewise designed as a loop. By application of heat, the shape-memory metal, for example nitinol, is provided with the impulse to close. The prosthesis loop then “remembers” its original state and is in this way secured on the process of the anvil. Consequently, this appears to be an elegant alternative to the push-on clip, which is slightly more expensive to produce, according to DE 296 09 687 U1 or DE 202 12 771 U1.
However, the known loop prostheses of the kind described in WO 02/0698590 A1 or U.S. Pat. No. 6,554,861 B2 have the considerable disadvantage that they completely enclose the corresponding point of attachment on the auditory ossicle, generally the process of the anvil or the manubrium of the hammer, which in practice can often lead to strangulation of the mucosa lying on the surrounded bone area and, consequently, to necrosis of the structures lying behind this.
Although this problem is solved by an auditory ossicle prosthesis according to EP 0 809 982 B1 from the Applicant, said prosthesis is once again a prosthesis with a clip acting as the securing element.
By contrast, the object of the present invention is now to design the known loop prostheses using the simplest possible means, in such a way that many different geometries and external diameters of the individual points of attachment in the middle ear of the respective patient can be covered with a single auditory ossicle prosthesis, while nonetheless avoiding complete strangulation of the point of attachment on the auditory ossicle and ensuring that the vessels inside the mucosa of the bone are not damaged or that they can follow a new path after the auditory ossicle prosthesis has been secured.
With an auditory ossicle prosthesis of the type defined at the outset, this complex object is achieved, according to the invention, in a surprisingly simple but effective manner, by virtue of the fact that the loop is designed in such a way that, after attachment of the auditory ossicle prosthesis, it bears with a force fit on the engaged member via at least three inner areas, and that, in the circumferential direction around the engaged member, at least three inner areas of the loop, one of which can comprise the slit-like or slit-shaped aperture, do not touch the member engaged by the loop but instead each extend at a distance from the surface of the engaged member, and in which the inner areas bearing on the engaged member and the inner areas of the loop not touching the engaged member each alternate in the circumferential direction around the engaged member.
In this way, without major technical outlay and in a simple way, the advantages of the above-described known auditory ossicle prosthesis of WO 02/069850 A1 or of U.S. Pat. No. 6,554,861 B2, which define the generic type, can be made use of, while at the same time neatly avoiding their important disadvantages compared to the prostheses according to documents DE 296 09 687 U1, DE 202 12 771 U1 or EP 0 809 982 B1. As in the “push-on clip with gaps”, which is slightly more complicated and expensive to produce, the modified loop of the first securing element of the auditory ossicle prosthesis according to the invention touches the supply vessels on the auditory ossicle only in the bearing areas. The other vessels run in the areas where the loop does not bear on the auditory ossicle, with the result that the supply of nutrients to the auditory ossicle, for example the long process of the anvil and the lenticular process, is not endangered.
A particularly preferred embodiment of the auditory ossicle prosthesis according to the invention is distinguished by the fact that the loop is constructed from flat band material and bears flat on the engaged member of the ossicular chain, as a result of which the pressure exerted locally by the securing element on the bone is distributed over a large surface area and in this way can be quite considerably reduced. In this way, it is possible to avoid the formation of constrictions and, therefore, the potential development of local necrosis.
Alternatively, however, the loop can also be constructed from wire material, which simplifies production, but can still entail the disadvantages described above.
These disadvantages can be avoided, or at least largely alleviated, in developments of this simple embodiment in which the wire material has a rectangular cross section, and the loop bears with a rectangle surface on the engaged member of the ossicular chain. In this way, as also in the case of the loop made from band material, the surface contact and the pressure exerted on the bone is distributed and locally reduced.
Embodiments of the invention are very particularly preferred in which the bearing points of the securing element on the auditory ossicle are distributed such as to ensure signal transmission free from distortion. This can be achieved by the fact that the areas via which the loop bears with a force fit on the engaged member of the ossicular chain are distributed symmetrically about the circumference of the engaged member.
In the auditory ossicle prosthesis according to the invention, the loop is generally arranged at one end of an elongate shaft that connects the loop to the other end of the auditory ossicle prosthesis, as is well known per se from the prior art.
In a geometrically particularly preferred development of this class of embodiments, an area via which the loop bears with a force fit on the engaged member of the ossicular chain is arranged in direct continuation of the shaft at the loop end of the latter. In this way, in the direction of the signal transmission through the auditory ossicle prosthesis, a force is introduced free of torque directly at the location of the mechanical attachment of the first securing element to the auditory ossicle.
In developments of the above embodiments, provision can alternatively or additionally be made that an area via which the loop bears with a force fit on the engaged member of the ossicular chain is arranged, in relation to the engaged member, lying diametrically opposite the direct continuation of the shaft at the loop end of the latter, as a result of which a favorable introduction of force during signal transmission is again achieved.
Other developments of the above-described class of embodiments are distinguished by the fact that an area that can comprise the slit-like aperture of the loop, and that does not touch the member of the ossicular chain engaged by the loop, is arranged in direct continuation of the shaft at the loop end of the latter.
After the prosthesis according to the invention has been placed surgically in the middle ear and the tympanic membrane has been closed again, the so-called incorporation phase starts. During this period, scars form and generate unpredictable forces, which can lead to the prosthesis shifting from its local position. For this reason, it is very useful if, after the operation, the prosthesis is able to compensate independently for a changed position in the middle ear. Since the anatomical features of the ear, for example the position, shape and size of the stirrup, anvil, hammer and tympanic membrane, also vary between individuals, it is generally very advantageous if auditory ossicle prostheses are not made rigid, but instead have a certain flexibility or variability. To achieve this flexibility or variability, various securing and coupling devices for auditory ossicles are known that have elastic parts and/or hinges. Such a hinged connection between a securing element, mounted on the footplate of the stirrup, and an elongate shaft of the auditory ossicle prosthesis is described per se in EP 1 181 907 B1 and is offered by the Applicant under the brand name “Ball-Joint-Prothese”. In a particularly preferred embodiment of the auditory ossicle prosthesis according to the invention, at least one ball joint is therefore provided on or in the elongate shaft.
In addition to the post-operative change of position, a further problem also arises after implantation of auditory ossicle prostheses. This is due to the fact that the middle ear of the human body constitutes a “semi-open bearing”. Any implantation material introduced into the body, in the context of a reconstruction of the middle ear and of its structures, is therefore subject to a particular stress arising from the fact that it lies in a contaminated and infected environment, which generally attacks the material. Since the aim of implanting an auditory ossicle prosthesis must be that the implant remains in the patient's middle ear for as long as possible and without complications, a protracted attack of the material can lead to damage of the prosthesis and/or to local infection. Both consequences are unacceptable. To prevent damage of the implanted material and also of the surrounding tissue on a permanent basis, another particularly preferred embodiment of the invention involves a biologically active coating, in particular a coating that inhibits growth and/or promotes growth and/or has an antibacterial action, being provided at least in some areas of the surface of the auditory ossicle prosthesis.
The auditory ossicle prosthesis according to the invention or parts thereof can be made of titanium and/or of tantalum and/or of steel and/or of an alloy of said metals. In addition to its strength and excellent sound conduction properties, the material titanium in particular is also known to have excellent biocompatibility in the middle ear in humans.
In view of the above-mentioned post-operative adjustment of position, embodiments of the invention are advantageous in which the prosthesis or parts thereof, in particular the loop, is made of a material with shape memory or with superelastic properties, preferably nitinol, which is known per se from, for example, the documents cited at the outset, namely WO 02/069850 A1 or U.S. Pat. No. 6,554,861 B2.
However, embodiments of the invention are also possible in which the prosthesis or parts thereof is/are made of biocompatible plastics, in particular silicone, polytetrafluoroethylene (PTFE) or composite fiber materials. Post-operative rejection reactions can also in most cases be avoided using these materials.
An embodiment of the device according to the invention is particularly preferred in which the weight distribution of the individual parts of the prosthesis is calculated as a function of a desired, predefinable frequency response of the sound conduction in the middle ear. It is thus possible, without major additional technical outlay, to achieve a degree of tuning of the sound propagation properties by means of an individually configured auditory ossicle prosthesis.
Such a tuning effect can be achieved, in particular embodiments, by the fact that at least one additional weight is secured on a part of the ossicular chain or of the prosthesis as a function of a desired, predefinable frequency response of the sound conduction in the middle ear.
In advantageous developments of these embodiments, the additional weight is secured on a part of the ossicular chain or the prosthesis by means of a clip. In addition, the additional weight and/or the clip can also be coated with a biologically active coating.
Depending on the individual defect that is to be remedied in a patient by use of the auditory ossicle prosthesis according to the invention, or that is at least to be alleviated in terms of its effects, the construction of the prosthesis is designed accordingly. In many embodiments, for example, the prosthesis can be secured at one end to the process of the anvil and at the other to the stirrup, or it can be plunged directly into the inner ear. In still further embodiments of the invention, the prosthesis is secured at one end to the manubrium of the hammer and at the other end to the anvil or to the stirrup, or is plunged directly into the inner ear. In this connection, an advantageous design is one in which the auditory ossicle prosthesis is located at the end point of the hammer (umbo) or directly next to it, as a result of which the maximum lever action is achieved for mechanically transmitting sound through movements in the artificial or natural ossicular chain. Other particularly preferred embodiments of the device according to the invention are distinguished by the fact that the auditory ossicle prosthesis is at one end coupled directly to the inner ear, in particular via a plunger, by means of perforation of the footplate of the stirrup (stapedectomy or stapedotomy) and/or by means of opening the human cochlea (cochleotomy).
In alternative embodiments of the auditory ossicle prosthesis according to the invention, the other end of the prosthesis remote from the loop can be provided with a second securing element, particularly also designed as a loop, as a closed bell, as a bell with one or more slits, or as a clip, for mechanical connection to a further member of the ossicular chain.
In further, particularly simple embodiments, the other end of the prosthesis remote from the loop is provided with a second securing element, designed in particular as a stamp or simple wire, for mechanical connection to the footplate of the stirrup without perforation.
A further embodiment of the invention, finally, is distinguished by the fact that the prosthesis is connected to an active vibration part of an active, in particular implantable hearing aid. In this way, further hearing damage can also be largely remedied by application of modern electronics or can at least be substantially alleviated in terms of its effects, in which case, on account of the above-described coating, a physical connection of the prosthesis to the outside world does not cause any problems resulting from increased bacterial ingress into the area of the middle ear, if the coating is made suitably antibacterial.
Further features and advantages of the invention will become clear from the following detailed description of illustrative embodiments of the invention, from the figures in the drawing, which shows important details of the invention, and also from the claims. The individual features can each be realized singly or in any desired combinations in variants of the invention.